APS April Meeting 2016
Volume 61, Number 6
Saturday–Tuesday, April 16–19, 2016;
Salt Lake City, Utah
Session U4: New High Energy Views of the Galaxy
3:30 PM–5:18 PM,
Monday, April 18, 2016
Room: Ballroom C
Sponsoring
Unit:
DAP
Chair: Julie McEnery, NASA
Abstract ID: BAPS.2016.APR.U4.3
Abstract: U4.00003 : NuSTAR results from the Galactic Center -- diffuse emission
4:42 PM–5:18 PM
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Abstract
Author:
Charles Hailey
(Columbia University)
The Nuclear Spectroscopic Telescope Array (NuSTAR) was launched in June
2012. It carried the first true, hard X-ray (\textgreater \textasciitilde 10
keV-79 keV) focusing telescopes into orbit. Its twin telescopes provide 10
times better angular resolution and 100 times better sensitivity than
previously obtainable in the hard X-ray band. Consequently NuSTAR is able to
resolve faint diffuse structures whose hard X-rays offer insight into some
of the most energetic processes in the Galactic Center. One of the
surprising discoveries that NuSTAR made in the Galactic Center is the
central hard X-ray emission (CHXE). The CHXE is a diffuse emission detected
from \textasciitilde 10 keV to beyond 50 keV in X-ray energy, and extending
spatially over a region \textasciitilde 8 parsecs x \textasciitilde 4
parsecs in and out of the plane of the galaxy respectively, and centered on
the supermassive black hole Sgr A*. The CHXE was speculated to be due to a
large population of unresolved black hole X-ray binaries, millisecond
pulsars (MSP), a class of highly magnetized white dwarf binaries called
intermediate polars, or to particle outflows from Sgr A*. The presence of an
unexpectedly large population of MSP in the Galactic Center would be
particularly interesting, since MSP emitting at higher energies and over a
much larger region have been posited to be the origin of the gamma-ray
emission that is also ascribed to dark matter annihilation in the galaxy. In
addition, the connection of the CHXE to the \textasciitilde 9000
unidentified X-ray sources in the central \textasciitilde 100 pc detected by
the Chandra Observatory, to the soft X-ray emission detected by the Chandra
and XMM/Newton observatories in the Galactic Center, and to the hard X-ray
emission detected by both the RXTE and INTEGRAL observatories in the
Galactic Ridge, is unclear. I review these results and present recent NuSTAR
observations that potentially resolve the origin of the CHXE and point to a
unified origin for all these X-ray emissions. Two other noteworthy classes
of diffuse structures in the Galactic Center will be discussed. The first
class are the giant molecular clouds, which are strong hard X-ray emitters.
These hard X-rays are believed to be produced when one or more giant
outbursts from the supermassive black hole Sgr A*, more than a century ago,
resulted in hard X-rays being reflected from the clouds, and detected only
today. I discuss how these hard X-rays are used to elucidate the past
history of the supermassive black hole, and to compare and contrast these
past giant outbursts with those observed from the supermassive black hole
more recently. The second class are non-thermal filaments, magnetized
structures with both radio and soft X-ray emission that have now been shown
by NuSTAR to be hard X-ray emitters. The electrons generating the hard
X-rays observed in one of these filaments are the most energetic that have
been observed in the galaxy. The filaments are a heterogeneous class of hard
X-ray emitters, and the various mechanisms by which they produce hard X-ray
emission will be discussed. Future NuSTAR observations of the Galactic
Center with NuSTAR will also be discussed.
To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2016.APR.U4.3